Resolved in: 4.0.0
Overview of the issue
Submitting the form in the secondary language fails. This producess the below console error:
xxxxx/wp-json?lang=es/contact-form-7/v1/contact-forms/XXX/feedback 404 (Not Found)
This issue occurs only when setting the language URL format to “Language name added as a parameter“.
Add this code to the theme’s functions.php file, found in the ../wp-content/themes/theme-name/ folder:
add_filter( 'wpcf7_load_js', '__return_false' );